which means that two Ising anyons can fuse into either the trivial particle/vacuum (indicated by \(I\) ) or into a regular fermion (indicated by \(\psi \) ). A less formal but equivalent way of viewing this is that the fusion (coupling and measurement) of two MBSs has two possible outcomes corresponding to the occupation of the fermion spanned by the measured MBS pair: empty, related to \(I\) , and full, related to \(\psi \) . The probability for each outcome depends on the joint state of the two MBSs. To experimentally demonstrate the fusion rules, one needs to initialize the system such that certain MBS pairs have a well-defined state and then measure the MBSs paired differently. Just like with braiding, the result is topologically protected and insensitive to the details of the measurement. Different methods have been proposed to demonstrate the MBS fusion rules [1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}.
<FIGURE>